1. Field of the Invention
Embodiments of the present invention relate, in general, to wireless network communications and particularly to parallel spectrum sensing and data services in wireless network communications.
2. Relevant Background
Wireless communication continues to be one of the greatest technology achievements. As communication systems continue to evolve and advance the spectral use of any one frequency resource has become increasingly important. As more and more frequency bands become occupied an emphasis has arisen to efficiently control and use each frequency resource.
In addition to efficiently controlling and using frequency bands assigned for wireless communication, the opportunity to use excess capacity of existing bands also exists. It is well known that television (“TV”) broadcast bands are, at any one instant, only utilized to 40% of their capacity. The remaining 60% can be used for other applications, services and spectral usage providing that the new signals do not interfere with the incumbent signal. Additionally the transition of analog TV signals to a digital format essentially opens the 700 MHz band for wireless use.
To use existing frequency bands for wireless communication, the incumbent signal must be sensed. Thus periodically a quiet time is established to determine whether the frequency band, also referred to herein as a channel, can continue to be used for other uses such as data services. One method for detecting incumbent signals is known to one skilled in the art as serial scheduling.
FIG. 1 shows a prior art depiction of a single channel in a wireless network being used for data services employing serial scheduling. In this depiction, a single channel 110 is being used to convey data services 120 as well as incumbent signals. Periodically sensing occurs to search for and detect, for example, an IEEE 802.22 Task Group 1 beacon 130 (also referred to herein as a TG1 beacon). A TG1 beacon essentially foretells the vicinity of an incumbent signal generator. While not the actual incumbent signal, the beacon protects another signal such as a FCC Part 74 Wireless Microphone signal that is or may be using the channel 110. After detection of the beacon 130 a quiet period 140 occurs to detect and capture the Master Super Frame (“MSF”) 150 of the beacon. The length of the quiet period 140 depends on what type, or the number, of MSFs being captured for the beacon. The capture of MSF1 can take 40 ms while capturing MSF1+MSF2+MSF3 can take as long as 100 ms. During this quiet/capture period, data services associated with the channel are interrupted. If during the quiet period the MSF(s) for that beacon is not captured, thus indicating that an incumbent signal is not present, the data services 120 are reestablished in a serial manner until the next beacon 130 is detected and the next quiet period 140 begins. As more MSFs 150 are captured, the interruption increases; however, the most significant interruption occurs when an incumbent signal (TG1 Beacon's MSF) is detected requiring the data services to be shifted to another channel.
FIG. 2 shows a prior art depiction of channel switching in a wireless network in which an incumbent signal is detected on a first channel. As in FIG. 1, FIG. 2 shows a channel 210 carrying data services 220. While the channel is carrying the data services 220 spectrum sensing occurs to detect a beacon 230. Upon detection of the beacon 230 a quiet period begins 240 interrupting the transmission of the data services 220. During the first quiet period 240 shown in FIG. 2 a beacon payload (MSF) is detected foretelling the presence of an incumbent signal 245. Accordingly the data services 220 must switch to another channel 270.
The switch to a new channel cannot occur immediately. At least two steps must occur to establish a new channel. First, data services 220 associated with the first channel 210 must initiate the move 260 to another channel and a new channel must be identified. Second, the newly identified channel 270 must be setup 280 to receive the data services 220. Once the new channel 270 is prepared, data services are reestablished and continue to be transmitted until another beacon payload is detected.
While the channel changing process occurs, data services are interrupted. The channel move initiation time associated with the first channel can take up to 2000 ms and the channel setup on the new channel can also take up to 2000 ms. Thus changing channels due to the detection of an incumbent signal can result in an interruption of services in excess of 4 seconds. Additionally, channel changes are not rare occurrences. While the new channel is selected because of its ability to carry the data services, it too carries incumbent signals. Thus while the new channel will be able to initially carry the data services, it is likely that the same issues forcing the initial channel change will occur again. Under the current serial scheduling techniques known in the prior art, each time a channel change is indicated, data services are interrupted for a significant period of time.